Detecting Multiple Simultaneous Force Inputs to an Input Device

1. An input device comprising: an input surface; and a processor configured to: determine, in response to a detected touch input to the input surface, a contact centroid relative to at least three points of contact on the input surface; determine a grouped contact centroid relative to a subset of the at least three points of contact; determine, based on a detected force input to the input surface, a grouped force vector relative to the contact centroid and the grouped contact centroid; assign a force input magnitude to each of the points of contact of the subset based, at least in part, on the grouped force vector; and providing each force input magnitude and the detected touch input as user input to an electronic device; wherein the subset comprises at least two points of contact; and the subset comprises at least one fewer point of contact than the at least three points of contact.

2. The input device of claim 1 , further comprising a multi-touch sensor coupled to the input surface, in communication with the processor, and configured to detect the touch input.

3. The input device of claim 1 , further comprising a force sensor coupled to the input surface, in communication with the processor, and configured to detect the force input.

4. The input device of claim 3 , wherein the force sensor comprises a set of force-sensitive elements coupled to the input surface.

5. The input device of claim 4 , wherein at least one force-sensitive element of the set of force-sensitive elements comprises a piezoelectric element.

6. The input device of claim 4 , wherein at least one force-sensitive element of the set of force-sensitive elements comprises a capacitive force sensor.

7. The input device of claim 1 , wherein the processor is configured to: determine a contact vector originating at the contact centroid and terminating at the grouped contact centroid; and determine a force projection vector by projecting the grouped force vector onto the contact vector.

8. The input device of claim 7 , wherein the processor is configured to: associate a first and a second contact force with each of the at least two points of contact based on the force projection vector.

9. An input device comprising: an input surface; a touch input sensor disposed below the input surface; a force input sensor disposed below the input surface; and a processor in communication with the touch input sensor and the force input sensor and configured to: determine, based on output from the touch input sensor, a contact centroid relative to at least three points of contact on the input surface; determine, based on output from the force input sensor, a force magnitude and a force centroid applied to the input surface; determine individual contact vectors, each originating at the contact centroid and each associated with a respective one of the at least three points of contact; determine individual force vectors, each originating at the contact centroid and each associated with a respective one of the at least three points of contact; determine a grouped contact centroid relative to a subset of the at least three points of contact; determine a grouped force vector relative to the contact centroid and the grouped contact centroid; adjusting at least two of the individual force vectors based on the grouped force vector; and providing each individual force vector and the output of the touch input sensor as user input to an electronic device; wherein the subset comprises at least two points of contact; and the subset comprises at least one fewer point of contact than the at least three points of contact.

10. The input device of claim 9 , wherein the force input sensor comprises a set of four force sensors.

11. The input device of claim 10 , wherein the set of four force sensors are distributed relative to a periphery of the input surface.

12. The input device of claim 10 , wherein the input surface is rectangular and the set of four force sensors are positioned at each corner of the input surface.

13. The input device of claim 10 , wherein the set of four force sensors are formed from a piezoelectric material.

14. The input device of claim 9 , wherein the input surface comprises glass.

15. A method of operating an input device comprising a touch input sensor and a force input sensor disposed below an input surface, the method comprising: detecting, with the touch input sensor, at least three points of contact on the input surface; determining a contact centroid of the at least three points of contact; determining, with the force input sensor, a force magnitude applied to the input surface; grouping two points of contact and determining a grouped contact centroid and a contact vector originating at the contact centroid; assigning a first input force to the group based on the force magnitude and the contact vector; and assigning a second input force to points of contact not in the group based on the force magnitude, the first input force, and the contact centroid.

16. The method of claim 15 , wherein grouping two points of contact comprises selecting two points of contact adjacent to one another.

17. The method of claim 15 , wherein assigning the first input force to the group comprises: determining a force centroid of the at least three points of contact; determining a group force vector based on the contact centroid; and projecting the group force vector onto the contact vector.

18. The method of claim 17 , further comprising: determining a force difference between the force magnitude and the first input force and the second input force; and evenly dividing the difference between the group and the points of contact not in the group.

19. A method of determining individual contact forces of multiple force inputs provided to an input device comprising a processor, a touch input sensor and a force input sensor, the method comprising: determining, by the force input sensor, a total force applied to an input surface of the input device; determining, by the processor of the input device, a force centroid based on the total force and locations of one or more force sensors of the force input sensor; determining, by the touch input sensor, individual contact centroids of at least three contact locations and combined contact centroid; determining individual contact forces, by the processor of the input device, based on the force centroid and the total force, along individual contact vectors defined from the combined centroid to each respective individual contact centroid; determining, by the processor of the input device, a largest individual contact force from the determined individual contact forces; determining, by the processor of the input device, a difference between the largest individual contact force and the total force; and dividing, by the processor of the input device, the determined difference evenly among all remaining contact locations that are not associated with the largest individual contact force.